I'd like as many of these features as possible:
A Wordpress plugin that, when installed and configured,
- Turns all existing WP members into forum members, and handles all future account creation through XF (already possible on one URL, but not across multiple blogs on different domains, as far as I'm aware)
- When installed, creates a category for each blog, a sub-category for every category of posts within each blog, and a new thread whenever a post is added to WP.
- Comments on posts are handled by XF, but are displayed below the blog post (similar to Disqus handling comments).